<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>17-进度条案例</title>
  <style>
    .bar {
      width: 300px;
      height: 20px;
      margin: 100px auto;
      border: 1px solid red;
      border-radius: 10px;
      padding: 1px;

    }

    .bar_in {
      width: 50%;
      height: 100%;
      background-color: red;
      border-radius: 10px 0 0 10px;
      /* 过渡效果：谁做过渡给谁加 */
      transition: all 2s;
    }

    .bar:hover .bar_in {
      border-radius: 10px 10px 10px 10px;
      width: 100%;
    }
  </style>
</head>

<body>
  <div class="bar">
    <div class="bar_in"></div>
  </div>
</body>

</html>